Method for Manufacturing an Emi Shielding Element

ABSTRACT

A method for manufacturing an EMI shielding element from a sheet of polymer material includes forming the shielding element by vacuum- or pressure-molding. The formed element is then chemically etched to roughen its surface on a microscopic scale. The surface is subsequently treated with a catalyzing solution to enable the shielding element to be plated by electroless plating. A first metallic layer is deposited on the etched and catalyzed surface by electroless plating, and a second metallic layer is deposited on the first by electrolytic plating.

BACKGROUND OF THE INVENTION

The present invention relates to shielding elements for electronicequipment, such as telecommunications, fiberoptic and computer equipmentand the like. The shielding elements are required to shield componentsof such equipment and connections thereto from electromagnetic fieldswhich may interfere with their operation.

In the prior art, shielding elements of this type have been formed frommetallic sheets by cutting and bending them into a desired cover-likeshape. In addition, shielding elements have been formed from plastic byinjection molding, and subsequently plated with metallic layers whichprovide the required shielding.

The present invention is an improvement over these prior-art methods byproviding a more economical method for manufacturing shielding elementsof this type.

SUMMARY OF THE INVENTION

Accordingly, the present invention is a method for manufacturing ashielding element for use in providing EMI (electromagneticinterference) shielding for electronic equipment by catalyzing andplating a sheet of polymer material formed by pressure or vacuum intothe shape of the shielding element.

The method includes the step of etching the part, as the shieldingelement is known during the manufacturing process, the part being formedfrom the sheet of polymer material to roughen its surface on amicroscopic level to enable it to be catalyzed and to enable a metalliclayer to adhere to it. The etched surface is then catalyzed with acatalyzing solution to enable it to be plated by electroless plating.

Electroless plating is used to deposit a first metallic layer on thesurface of the part. The first metallic layer may be of any conductivemetal, including copper, nickel, cobalt, silver, gold or tin, andrenders the part electrically conductive, so that it may function as acathode in a subsequent electrolytic plating step.

Finally, electrolytic plating is used to deposit a second metallic layeron the surface of the part over the first metallic layer. The secondmetallic layer may be of any electrolytic metal including nickel, tin,copper, zinc or chromium.

The present invention will now be described in greater detail in thediscussion that follows.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The shielding elements which are manufactured in accordance with themethod of the present invention have a wide variety of uses in theelectronics industry, where they are generally used for EMI shielding.As such, they have a wide variety of shapes and configurations to enablethem to carry out a desired shielding function for a particularapplication. For example, a shielding element may be a cover for a chipon a circuit board within a piece of electronic equipment, or it may bea cover or housing for an entire component within a piece of electronicequipment, such as a personal computer. In addition, the shieldingelement may be an enclosure for a cable connection to a piece ofelectronic equipment. In short, the present invention is not limited toa shielding element of any one of these specific varieties, but isintended to cover all of these as well as others not explicitlyidentified here.

In accordance with the present invention, the shielding elements arepressure- or vacuum-molded from sheets of polymer material, rather thaninjection-molded following the established procedures of the prior art.The polymer material, in sheet form, may be of any variety, includingTEFLON® (polytetrafluoroethylene), polyester or polypropylene, but ispreferably of ABS (acrylonitrile-butadiene-styrene copolymer), HIPS(high-impact polystyrene) or PC-ABS (polycarbonate ABS), which arepreferred as they are readily susceptible to standard catalyzation andplating procedures. A suitable ABS plastic is available from BayerCorporation of Elkhart, Ind., USA as Lustran 752, which is ahigh-impact, high-gloss, black ABS plastic provided in sheet form havinga thickness of 17 mils (0.017 inch; 0.43 mm). LUSTRAN® is a registeredtrademark (U.S. Registration No. 720,161) owned by Bayer Corporation.

In order to be formed into a shielding element of a desiredthree-dimensional geometry, the sheet of polymer material is cut into asize that will fit into the forming apparatus to be used, that is,either a pressure- or vacuum-molding apparatus. The sheet is heatedslightly, so that it may be softened and readily deformable, and placedbetween the two dies of the mold in the forming apparatus. The mold isthen closed and either pressure or vacuum is used to make the polymersheet conform to the shape of the mold. The “part” thereby obtainedretains that shape upon removal from the mold. It will be appreciatedthat the “part” will have both formed portions, which will eventuallybecome the shielding element being manufactured, and unformed portions,these being areas of the sheet not deformed in the molding apparatus.These latter portions may be trimmed from the shielding element asnecessary, perhaps at the end of the plating process.

The next step in the manufacturing process is to clean the part to beplated to remove any oil, grease or other contaminant it may haveacquired during forming. For example, the part may be cleaned by dippingit into 1-propanol (propyl alcohol) at room temperature for thirtyseconds, and then rinsed in running DI (deionized) water to remove anyalcohol film remaining on the part after dipping. More generally, anycommercially available solvent, such as an alcohol, may be used in thecleaning step.

The manufacturing process proceeds with an etching step, in which thesurface of the part is roughened on a microscopic level to prepare itfor catalyzation and plating. A chrome/sulfuric acid etching solutionmay be used for this purpose.

Such a solution may be prepared by dissolving 380 grams of chromic acidin DI water sufficient to produce a solution having a volume of 830 ml.Then, 170 ml of concentrated sulfuric acid are added to bring the volumeto 1 liter.

The resulting solution is heated to 70° C., and mechanically stirredwhile the part is immersed for approximately seven minutes. The part isthen removed and rinsed under running DI water until chromium is nolonger visibly present on its surface.

In the next step, namely, the catalyzing step, the etched surface of thepart is catalyzed to enable it to be plated by electroless plating. Acommercially available catalyzer may be used for this purpose. Forexample, Shipley Cataposit 44, available from the Shipley Company ofMarlboro, Mass., USA, may be used. CATAPOSIT® is a registered trademark(U.S. Registration No. 1,031,891) owned by Rohm and Haas Company ofPhiladelphia, Pa., USA.

A catalyzing solution for the present manufacturing process is preparedby diluting 50 ml of Shipley Cataposit 44 with sufficient DI water toproduce a volume of 300 ml. The resulting catalyzing solution is thenheated to 40° C., and mechanically stirred while the part is immersedtherein for one minute. The part is then removed and immersedsequentially in three containers of DI water, the part being left in thethird container until the next step in the manufacturing process is tobe performed.

Shipley Cataposit 44 uses a tin and palladium mixture as the catalyzer.Other catalysts employing palladium, gold, silver or platinum may alsobe used in the practice of the present invention.

The next step is an electroless plating step. A commercially availableelectroless plating solution may be used for this purpose. For example,MacDermid Ultra Dep 1000 electroless copper, available from MacDermidIncorporated of Waterbury, Conn., USA, may be used. To carry out theelectroless plating step, a suitable amount of MacDermid Ultra Dep 1000electroless copper solution is prepared, heated to 50° C., andmechanically stirred while spare catalyzed material is plated for 15 to20 minutes to activate the solution. The spare material is then removed,and the part to be plated is then immersed in the solution, which isstill being mechanically stirred, and plated for approximately sevenminutes. The part is then removed and rinsed under running DI water.

Alternatively, the electroless plating step may be performed withelectroless plating solutions based on nickel, cobalt, silver, gold ortin without departing from the scope of the present invention.

The final step in the manufacturing process of the present invention isan electrolytic plating step. A commercially available electrolyticplating solution may be used for this purpose. For example, MacDermidBarrett SN (electrolytic sulfamate nickel), also available fromMacDermid Incorporated of Waterbury, Conn., USA, may be used. To carryout the electrolytic plating step, a suitable amount of MacDermidBarrett SN is prepared, heated to 50° C., and, adjusted to have a pH of4.0. A standard Hull-cell nickel anode is then mounted in theelectrolytic plating solution, which is mechanically stirred. The partis then plated at 2.0 amps for approximately 2 minutes, rotated by 180°,and plated for an additional approximately 2 minutes at 2.0 amps. Thepart is then removed from the solution, rinsed in running DI water, anddried at 80° C. for 30 minutes.

While nickel is most commonly used in electroplating because of itscorrosion resistance, the electrolytic plating step could alternativelybe used to apply a layer of tin, copper, zinc or chromium onto the part.All of these metals are useful in providing EMI shielding.

Modifications to the above would be obvious to those of ordinary skillin the art, but would not bring the invention so modified beyond thescope of the appended claims.

1. A method for manufacturing a shielding element for use in providingEMI shielding for electronic equipment, said method comprising the stepsof: a) providing a sheet of a polymer material; b) forming a part havinga three-dimensional geometry desired for said shielding element fromsaid sheet of polymer material; c) etching said part to roughen thesurface thereof on a microscopic level; d) catalyzing said surface ofsaid part with a catalyzing solution to enable said surface to be platedby electroless plating; e) performing electroless plating on said partto deposit a first metallic layer on the surface thereof; and f)performing electrolytic plating on said part to deposit a secondmetallic layer on said first metallic layer.
 2. A method as claimed inclaim 1 wherein said polymer material is selected from the groupconsisting of polytetrafluoroethylene, polyester and polypropylene.
 3. Amethod as claimed in claim 1 wherein said polymer material is ABS(acrylonitrile-butadiene-styrene copolymer).
 4. A method as claimed inclaim 1 wherein said polymer material is HIPS (high-impact polystyrene).5. A method as claimed in claim 1 wherein said polymer material isPC-ABS (polycarbonate-acrylonitride-butadiene-styrene copolymer).
 6. Amethod as claimed in claim 1 wherein said part is formed from said sheetby pressure-molding.
 7. A method as claimed in claim 1 wherein said partis formed from said sheet by vacuum-molding.
 8. A method as claimed inclaim 1 further comprising, between steps b) and c), the step ofcleaning said part formed from said sheet of polymer material.
 9. Amethod as claimed in claim 8 wherein said cleaning step includes dippingsaid part in a solvent.
 10. A method as claimed in claim 9 wherein saidsolvent is 1-propanol.
 11. A method as claimed in claim 1 wherein saidetching step includes immersing said part in a chrome/sulfuric acidetching solution.
 12. A method as claimed in claim 11 wherein said partis rinsed under running deionized water following immersion in saidetching solution.
 13. A method as claimed in claim 1 wherein saidcatalyzing solution has a tin and palladium mixture as a catalyzer. 14.A method as claimed in claim 1 wherein said catalyzing solution has ametal selected from the group consisting of palladium, gold, silver andplatinum as a catalyzer.
 15. A method as claimed in claim 1 wherein saidelectroless plating includes immersing said part in an electrolessplating solution.
 16. A method as claimed in claim 13 wherein saidelectroless plating solution has a metal selected from the groupconsisting of copper, nickel, cobalt, silver, gold and tin as the metalbeing plated to deposit said first metallic layer.
 17. A method asclaimed in claim 1 wherein a nickel anode in a sulfamate nickel solutionis used in said electrolytic plating step to deposit nickel as saidsecond metallic layer.
 18. A method as claimed in claim 1 wherein ametal selected from the group consisting of nickel, tin, copper, zincand chromium is deposited by electrolytic plating as said secondmetallic layer.